This invention relates to an improved doctor-blade assembly for a flexographic press. A flexographic press is a roll press used for imprinting images using a quick-drying ink in a continuous feed process. Flexographic printing utilizes an ink-metering roller that picks up ink from an ink pan and transfers a metered quantity of ink to a plate cylinder with image areas in relief. The plate cylinder transfers the image to a substrate that passes between the plate cylinder and an impression cylinder that backs up and supports the substrate as it contacts the printing plate. The contact pressure must be precisely adjusted such that the contact point or nip between the two cylinders provides a "kiss" impression that transfers the ink to the substrate.
The ink metering roller, also called the anilox roll, has a surface that is engraved with tiny uniform cells or pockets that carry and deposit a thin uniform ink film onto the plate cylinder. In some configurations of a flexographic press, the ink is metered to the anilox roll by a separate fountain roll that picks up the ink from the ink pan and transfers it to the anilox roll in a contact transfer that squeezes out excess ink, which returns to the ink supply pan. In more modern configurations, the anilox roll serves as the dual function of a fountain roll and metering roller by use of a doctor blade, which is an elongated metal blade or knife that shaves excess ink off the anilox roll, leaving only ink in the recess cells.
For color printing, a press station having a separate ink tray, anilox roll, plate cylinder, and impression cylinder is required for each color ink used for the final composite work. Flexographic printing has certain advantages that make it useful in product packaging where a variety of different composition substrates are employed, or more recently, in newspaper printing where water-base inks are utilized to produce newsprint that does not rub off on the hands of the reader.
Flexographic presses are generally large in size and the plate cylinder frequently carries multiple plates for a single printing run. It is, therefore, advantageous to split the ink fountain tray into sections for inking with different color or different composition inks. Frequently, flexographic presses are installed with an ink fountain tray that is divided into two equal sections. Conventional means for dividing the fountain tray utilize a laminated fountain splitter. The laminated fountain splitter has a closed cell foam backing to provide contact pressure from compression, a stiff arcuate substrate and a TEFLON (tetrafluoroethylene contact surface. The TEFLON wiping surface fails to prevent cross-bleed of inks and ultimately results in excessive scoring of the anilox roll. Replacement of the anilox roll is both time consuming and expensive.
The improved doctor-blade assembly of this invention includes features that assist in maintaining proper alignment of the ink fountain tray and sealing of the fountain tray with the anilox roll when the fountain tray is moved into place. Furthermore, the ink fountain in the doctor-blade assembly of this invention utilizes a fountain splitter of improved design that inhibits cross-bleed and eliminates scoring or excess wear on the anilox roll. While the term, doctor-blade assembly, has been used in the art to define only the assembly of the customary two opposed doctor blades and their attachment means to an ink fountain, in this specification the doctor-blade assembly includes the ink fountain, the doctor-blade sub-assembly and the actuating mechanism connecting the ink fountain to the press unit.